Digitizing method

ABSTRACT

A digitizing method in which a distance from a model surface is measured and stored at regular intervals of time or distance to obtain digital profile data of the model. A specified profile for correction is provided on a part of the model, and by using the specified mode, correction data such as a distance correction coefficient is obtained before carrying out the digitizing. Digitizing data obtained by carrying out the digitizing is corrected by the correction data. The correction data is obtained based on the material and surface condition of the actual model, and therefore, the digitizing data can be accurately corrected.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to a digitizing method using a non-contacttype range finder such as a laser range finder, and more particularly,to a digitizing method in which a specified profile is provided on apart of a model to obtain correction data for correcting digitizingdata.

BACKGROUND ART

A digitizing method has been proposed which comprises irradiating alaser beam onto the surface of a model, measuring the distance from themodel surface through detection of the reflected laser beam, and whileperforming a follow-up control to maintain the distance from the modelsurface at a constant value, reading a machine position of each axis atregular intervals of time or distance for storage in a memory.

The reflectivity of the model surface and the scattering rate of thereflected wave may vary in accordance with the material of the modelused, thereby causing significant errors in measurements by a detectionsignal from a range finder, and thus lowering the accuracy of digitizingdata. Accordingly, it is to obtain accurate digitizing data unless thematerials and surface conditions of models are limited.

SUMMARY OF THE INVENTION

The object of the present invention is to solve the aforementionedproblems and provide a digitizing method in which a specified profile isprovided on a part of a model to obtain correction data for correctingdigitizing data.

To solve the above problems, the present invention provides a digitizingmethod in which a distance from a surface of a model is measured andstored at regular intervals of time or distance to obtain digitalprofile data of the model, comprising

providing a specified profile for correction on a part of the model,

issuing a measurement command and obtaining correction data such as adistance correction coefficient, a zero point correction value, and thelike from a command value and an actually measured value, by using thespecified profile, before the start of digitizing, and

correcting digitizing data obtained by carrying out the digitizing, bythe correction data.

Using the specified profile provided on a part of the model beforecarrying out the digitizing, a constant distance command is issued andcorrection data is obtained from the command value and actualmeasurement data.

Therefore, the correction data is obtained based on the material andsurface condition of the actual model, it is possible to accuratelycorrect the digitizing data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a device for carrying out a digitizingmethod according to the present invention;

FIG. 2 is a diagram showing a specified profile provided on a model;

FIG. 3(a) is a diagram showing an example of the specified profile;

FIG. 3(b) is a diagram showing another example of the specified profile;

FIG. 4 is a diagram for illustrating how correction data is obtainedwith the specified profile of FIG. 3(a);

FIG. 5 (a) and FIG. 5(b) are flowcharts for obtaining correction anddata; and

FIG. 6 is a flowchart of a digitizing method according to one embodimentof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the present invention will now be described withreference to the drawings.

FIG. 1 is a block diagram of a device for carrying out a digitizing datacorrection method according to the present invention. In FIG. 1, numeral1 denotes a processor for global control, 2 denotes a timer forinforming the processor 1 of an elapse of time, and 3 denotes a memoryincluding a ROM storing a control program, a RAM for storing variousparameters, data, etc., and the like An input/output signal interface(I/O) 4 carries out an exchange of input/output signal with an outsidesource, and an AD converter 5 converts an analog signal from a rangefinder 10 into a digital signal. Denoted at 6x, 6y, and 6z are DAconverters for X, Y, and Z axes, respectively, for converting digitalcommand values written by the processor 1 into analog values as outputs,and 7x, 7y, and 7z denote counters for the X, Y, and Z axes,respectively, which detect feedback pulses from a position detector(described below) and convert those pulses into data readable by theprocessor 1.

Servo amplifiers 8x, 8y, and 8z for the X, Y, and Z axes, respectively,receive analog signals from the DA converters 6x, 6y, and 6z to driveservomotors 9x, 9y, and 9z.

A range finder 10, which is a laser range finder in this embodiment,radiates a laser beam onto a model, receives a beam reflected by a model13, and produces and delivers a voltage signal corresponding to thedetected distance, to the AD converter 5 A column head 11 is constructedin such a manner that the range finder 10 can be moved vertically by theservomotor 9z. Denoted at 12 is a table on which the model 13 issecured; movements of which are controlled by the servomotors 9x and 9y.An operator panel 14 is used by an operator to control a machine, and asignal therefrom is connected to the input/output interface (I/O) 4.

The aforementioned servomotors are connected to respective positiondetectors 15x, 15y, and 15z, the output pulses of which are input to thecounters 7x, 7y, and 7z.

A specified profile provided on the model 13 will now be described. FIG.2 shows a specified profile provided on the model, wherein 13 denotesthe model to be digitized, 13a a measurement range for the digitizing,and 13b the specified profile.

FIG. 3(a) shows an example of the specified profile, which is composedof a horizontal plane and a plane inclined at 45 degrees to the model.Correction data can be obtained from these two planes, as describedhereinafter in detail.

FIG. 3(b) shows another example of the specified profile, which includesa horizontal plane and several planes inclined at different angles tothe model surface. Correction data is obtained from each of theseplanes, and the obtained data is used for the corresponding plane of themodel.

The procedure used to obtain the correction data will now be describedin detail. FIG. 4 illustrates how the correction data is obtained withthe specified profile 13b shown in FIG. 3(a). In FIG. 4, the rangefinder 10, which is a laser range finder in this embodiment, is firstpositioned at a point P1 on the plane of the specified profile 13b,through an operation of a button on the operator panel 14. Subsequently,the operator panel 14 is set in a measurement mode, and a start buttonis depressed to start a measurement operation.

The Z axis is first moved by a distance L_(O) in the +Z direction and adetection distance L from the range finder 10 is read, and then the Zaxis is further moved in the +Z direction by ΔL and a detection distanceLa from the range finder 10 is read.

Next, the Z axis is moved and is positioned at a point P2, then as forthe measurement based on the point P1, the Z axis is moved in the +Zdirection by L_(O) and ΔL to read a detection distance Lb, and as aresult, a zero point compensation can be obtained from the followingequation:

    ΔE=L.sub.O -L

Subsequently, the distance correction coefficients are calculated.Namely, a correction coefficient for horizontal plane including thepoint P1 is obtained by

    CfO=La/(L.sub.O +ΔL)

and a correction coefficient for the 45-degree inclination planeincluding the point P2 is obtained from

    Cf45=Lb/(L.sub.O +ΔL)

Based on the results of these calculations, a mean value Cfm of thesetwo correction coefficients is obtained and used to correct a measuredvalue of the range finder 10. Specifically, for an actually measureddistance data L, a true value Lac is obtained from

    Lac=(L-ΔE)/Cfm

The above operations will now be described with reference to FIG. 5(a)and FIG. 5(b) illustrating flowcharts for obtaining the correction data.In the figures, the number following "S" represents the number of thestep, and only those operations after the positioning of the rangefinder 10 at the point P1 in FIG. 3 are explained in the flowcharts.

[S1]The Z axis is moved in the +Z direction by L_(O).

[S2]The distance signal L is read.

[S3]The zero point correction amount ΔE=L_(O-L) is calculated.

[S4]The Z axis is moved by ΔL.

[S5]The distance signal La is read.

[S6]The correction coefficient is calculated by the following equation:

    CfO=La/ (L.sub.O +ΔL)

[S7]The range finder 10 is moved to the point P2 in FIG. 3, and then theZ axis is moved in the +Z direction by (L_(O) +ΔL).

[S8]The distance signal Lb is read. [S9]The correction value for the45-degree inclination plane is obtained by the following equation:

    Cf45=Lb/(L.sub.O +ΔL)

[S10]The mean value Cf of the above-mentioned correction coefficients isobtained by the following equation:

    Cf=(CfO+Cf45)/2

and thus the correction coefficient is obtained.

A digitizing operation using this correction coefficient will now bedescribed with reference to FIG. 6, which is a flowchart of thedigitizing method. In the figure, the number following "S" representsthe step number.

[S11]The distance L and amounts ΔX, ΔY, ΔZ of movement of the respectiveaxes are read.

[S12]The distance ΔZ is corrected by the following equation:

    Lr=(L-ΔE)/Cf

[S13]An error is calculated by the following formula:

    ΔL=Lr-L.sub.O

[S14]Speeds of the respective axes are calculated and commandedaccordingly.

[S15]The digitizing data is collected.

In this manner, the data measured by the range finder 10 is correctedfor carrying out the digitizing.

In the foregoing description, a mean value of the two correctioncoefficients for the horizontal plane and the 45-degree inclinationplane is used as the correction coefficient, but another suitablecorrection coefficient may be used according to the model profile. Forexample, the specified profile shown in FIG. 3(b) may be used in such away that correction coefficients are obtained for the respective planesand are suitably used according to the model profile.

Furthermore, although the above description is based on the use of alaser range finder, other range finders can be used as long as they arenon-contact type.

According to the present invention, as described above, a specifiedprofile is provided on a part of the model and correction data forcorrecting a measurement error of the range finder is obtained on thebasis of the measurement of the specified profile. A measured distanceis corrected by this correction data and then digitizing is carried out,thus making it possible to obtain accurate digitizing data.

What is claimed is:
 1. A method for measuring a distance from a surfaceof a model, comprising the steps of:providing a specified profile on aportion of the model, for use in obtaining correction data; obtainingthe correction data based on the specified profile, said correction dataobtaining step including calculating a zero point correction amount anda mean value of a correction coefficient; measuring a distance from thesurface of the model to obtain measured data; and obtaining digitizeddata based upon the obtained measured data and the correction data.